you can use a regular atx power supply, that doesn't have the ATX+12V connector ... but rather than hacking something with a dremel, just get a molex to +12v adapter cable ... they're like $5 and will fit perfect.
psu manuf would lead you to believe the +12v connection is something special, and on really expensive psu it is ($150+), but on the ordinary psu, it leads back to the same capacitor all the yellow wires originate from... the single 12v rail.
what sets apart the $150-$500 psus is they have multiple 12v rails, one or more for periphals like drives, one solely for the switchmode power supply built into the motherboard that converts 12v down to 1.?v for the memory and processor(s) ... you mainly need this in a server that might have 2, 4 or more processors and 8-32 banks of ram